I can't answer the OPs question, because I'm not sure how other bikes (or Suzukis) behave when disconnecting the battery terminals, while operating the engine but I can offer the following:
1) There is no need as far as I can see, to disconnect the battery, as a test, to see if the charging system is working. Here's why: assume the battery sits at some voltage, say 13V while disconnected and when running the engine it's at a higher voltage, say 14.5V. If that's the case then it is being charged and the charge current going into the battery, is proportional to the voltage difference. That's why the service manual only specifies that the voltage should be at 14.5V, i.e. sufficiently higher than that of a freshly charged battery. Of course, if you turn on more loads, the voltage might drop, and that's why turning on the high beam during the test is specified. So if it sits at 14.5V with the high beam on, the generator can supply the needed current to run the bike and keep the battery charged and that's all we need to know.
2) Disconnecting a battery from a running generator can cause serious issues, as already stated. See here
, if you''re interested in more details. Note that the ensuing overvoltage doesn't need to fry anything right away. It can just put strain on wiring, connectors and devices (i.e. overheat them temporarily, enough to cause non-critical damage) that can accumulate, to cause premature failure. So practices such as these, can cause problems further down the road, making them look like random failures due to presumed design flaws or manufacturing problems.
3) I'm also not trying to pick a fight, but I must point out that, apart from "that guy" who reads the instructions, just to use a toothpick, there's also "that guy" who damages perfectly good equipment, because he feels he can perform maintenance, without knowing the basic operating principles of the equipment and/or proper procedures and why they should be followed. Perhaps that is one explanation for why there are pretty reliable used bikes out there, with heaps of miles on the clock, and others with heaps of problems and hardly any miles on the clock. For the sake of the bikes, if not for anything else, please, don't be that guy.